Reshaping the Flood? - Analyzing the Large Scale Impact of Reservoirs and Dams on Flood Reduction in Germany

Flood retention basins are a crucial element in flood protection strategies. Local studies have clearly demonstrated their effectiveness in significantly reducing flood discharges, thereby minimizing potential downstream damage. However, the impact of these retention basins on reducing flood discharges at the large river basin scale remains unclear.This study investigates the influence of reservoirs and dams on flood discharge reduction in Germany. Using the spatially distributed hydrological model SALTO, daily discharges from over 1500 gauged catchments between 1951 and 2020 were simulated. The model incorporates the effects of 530 reservoirs and flood retention basins on daily runoff volumes. Calibration at 700 gauging stations allows for regional parameterization of the model based on the PASS method. The study examines various scenarios, including the absence of reservoirs for flood protection and changes to the storage capacity and function of individual reservoirs. It not only assesses the reduction of runoff peaks but also analyzes changes in the duration of individual flood events and their spatial extent, considering the complex network of 530 reservoirs. In essence, this research contributes to the ongoing discourse on the effectiveness of flood retention basins and provides insights into the nuanced roles of reservoirs and dams in shaping the hydrological landscape. The findings offer valuable guidance for optimizing flood protection strategies, considering storage capacities, operational functions, and the broader spatial and temporal aspects of flood events.